<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>元素的层级</title>
    <style>
        body{
            font-size:50px;
        }
        .box1{
            width:200px;
            height:200px;
            background-color: aqua;
            position:absolute;
            /* z-index:1; */
        /*对于开启了定位的元素，可以通过z-index属性来指定元素的层级
        z-index需要一个整数作为参数，值越大元素的层级越高，元素的层级越高就越优先显示
        如果元素的层级一样，则优先选择越靠下的元素
        注意：祖先元素的层级再高，也不会盖住后代元素*/
        }
        .box2{
            width:200px;
            height:200px;
            background-color:rgba(0,0,0,.3);
            position:absolute;
            top:50px;
            left:50px;
            /* z-index:2; */
        }
        .box3{
            width:200px;
            height:200px;
            background-color:darkorchid;
            position:absolute;
            top:100px;
            left:100px;
            /* z-index:3; */
            /*注意：祖先元素的层级再高，也不会盖住后代元素*/
        }
        .box4{
            width:100px;
            height:100px;
            background-color: chartreuse;
            position:absolute;
        }


    </style>
</head>
<body>
    <div class="box1">1</div>
    <div class="box2">2</div>
    <div class="box3">3
        <div class="box4">4</div>
    </div>

    
</body>
</html>